The Turkish deployment appeared moderate in scale and seemed more defensive and preparatory -- and perhaps symbolic -- than offensive in nature.

Meanwhile, official Syrian state media reported a "terrorist explosion" Thursday in the parking lot outside a judicial complex in central Damascus, the capital. Television images from the scene showed smoke billowing from the blast and firefighters with hoses dousing flames that appeared to have engulfed several parked cars.

There was no immediate word on casualties or damage in Thursday's explosion. Syria has suffered a number of car-bomb attacks in recent months, mostly targeting government or security installations, that have left dozens of civilians dead. The government has blamed "terrorists," its label for anti-government forces.

Rebels seeking to oust Syrian President Bashar Assad have vowed to take the battle to the capital, and fierce clashes have been reported in recent days in Damascus' restive suburbs.

On Wednesday, gunmen stormed a pro-government television station outside the capital, ransacked the offices and studios, set off explosives and killed three journalists and several other employees, state media reported. Press organizations worldwide and the White House condemned the attack.

The raging conflict in Syria has reverberated across the border in Turkey, which shares a 500-mile frontier with its Arab neighbor.

Turkish media reported a convoy of about 30 military vehicles, including trucks with missile launchers, being deployed Thursday along the Syrian border in southern Hatay province.

Turkish officials have stressed that they want to avoid a military confrontation with Syria, but were enraged last week when Syrian forces shot down a Turkish military jet off Syria's Mediterranean coast. Turkish Prime Minister Recep Tayyip Erdogan has said border security would be bolstered and that any Syrian military units approaching Turkey would be regarded as a threat.

The Turkish military buildup, and the increasingly tense Turkish-Syrian relations, could raise the possibility of a border clash. The Turkish frontier zone has become a haven for Syrian rebels and is also home to tens of thousands of Syrian refugees who have fled the violence next door.

U.N. special envoy Annan has called an emergency meeting of what he calls the "Action Group for Syria" -- including the United States and the four other U.N. Security Council permanent members -- for Saturday in Geneva. The session is widely viewed as a last-ditch effort to salvage his six-point peace plan, widely violated by both sides.

U.S. Secretary of State Hillary Rodham Clinton said Wednesday that Annan seeks to lay down a "political transition road map" for Syria, where Assad’s forces have been battling a more than 15-month-old uprising. In comments to reporters in Helsinki, Finland, Clinton indicated the new "transition" plan could signal a breakthrough in the diplomatic logjam blocking any resolution of the Syrian crisis.

Reuters reported from the United Nations that Annan is proposing a "national unity Cabinet" that would apparently help facilitate a transitional government in Syria. There was no confirmation from Annan about the report.

The U.N. envoy said in a statement that leaders meeting Saturday "should agree on guidelines and principles for a Syrian-led political transition that meets the legitimate aspirations of the Syrian people, and agree on actions that will make these objectives a reality on the ground."

A major question of any transition blueprint is the fate of Assad, who has been digging in and warning the nation that it is on a war footing.

Washington and its allies say Assad must step down. But Russia and China have so far refused to go along with any international plan calling for his ouster.